This invention relates to a process chamber for processing semiconductor substrates, and in particular to a gas distributor for distributing process gas into the process chamber.
A process gas distributor that provides a non-uniform distribution of process gas in a process chamber can cause large variations in processing rates and uniformity across a surface of a substrate processed in the chamber. In semiconductor fabrication, process gas is introduced into the chamber and a plasma is formed from the process gas to etch or deposit material on the substrate. However, current semiconductor substrates have increased in diameter from 100 mm (4 inches) to 300 mm (12 inches). The proportionate increase in the volume of the chamber has made it more difficult to provide a uniform distribution of process gas or plasma species across the entire processing surface of the substrate. As a result, there is often considerable variation in processing rates and processing uniformity from the center to the periphery of the substrate.
Achieving a uniform process gas distribution is a particular problem in process chambers having ceramic walls or ceilings because it is difficult to fabricate the ceramic components with feed-throughs that allow gas nozzles to extend therethrough to uniformly distribute process gas into the process chamber. The ceramic walls are composed of polycrystalline ceramic material, such as aluminum oxide or silicon, which are brittle materials and difficult to machine holes for holding a gas feedthrough without breaking or otherwise damaging the ceramic component. Also, other components, such as RF induction coils, adjacent to the ceramic walls further reduce the space available for locating a gas nozzle through the wall. Thus there is a need for a gas distributor that provides a uniform distribution of process gas in a process chamber having ceramic walls or ceilings without requiring a hole or other feed-through to be drilled through the ceramic component.
Yet another problem with current process chambers is that a relatively large amount of process gas is required to provide uniform processing rates across the substrate as compared to the amount of process gas actually consumed during processing of the substrate. Conventional process chambers require an abundance of process gas to assure complete processing of the semiconductor substrates. For example, typical CVD processes are 30 to 68% efficient, which leaves 70 to 32% of the unconsumed process gas exhausted in the effluent gas. Typical etch processes are even less efficient and often use as little as 10% of the total volume of process gas. These inefficiencies in process gas utilization increase the processing cost per substrate, particularly when the process gas is expensive. Also, excessive emissions of unconsumed process gases necessitate some form of effluent abatement apparatus to reduce the toxic or environmentally hazardous compounds in the effluent process gas, which is also expensive.
Thus there is a need for a process chamber having a gas distributor that provides a uniform distribution of process gas in the chamber, particularly for large diameter substrates. There is a further need for a gas distributor that increases the efficiency of utilization of process gas in the chamber, and thereby reduces environmentally hazardous emissions. There is also a need for a gas distributor that does not require holes or feed-throughs in ceramic walls in order to provide a uniform distribution of gas in the chamber.